Rio Tinto admits red mud dam was unable to handle flood

RIO Tinto Alcan will be fined between $30,000 and $50,000 after admitting it did not have the capacity to cope with a big flood at its red mud dam at Yarwun last year.

Rio Tinto pleaded guilty on Wednesday to the breach of environmental obligations in Gladstone Magistrate's Court, with the resources giant and the Department of Environment and Heritage Protection agreeing to a fine of between $30,000 and $50,000.

As part of its obligations, Rio must have enough residue management area storage at its plant calculated based on expected rainfall from a one in 50-year, three-month-long wet season.

However, an investigation by the department found progress on an upgrade was too slow.

Rio has since met that capacity, and is on track to meet its 2013 capacity requirements.

A final verdict in the case was adjourned until Thursday afternoon.

Rio said it would not comment on the case until a verdict had been reached in the judicial process.

The dam contains waste from the process of making alumina.

As part of the process, caustic soda and alumina solution passes into rows of thickener tanks, where solid impurities sink to the bottom as a fine, red mud.

The impurities are washed several times with water and disposed of in tailings dams.